Block 2

Compound Angle Formulae

What is to be learned?

• How to deal with exam type questions involving compound angles formulas.

A

C

B

D

Write the exact value of sin DAB

3

5

LDAB = 90 + x

x

sin DAB = sin (90 + x)

Mark Angle

Write like a formula Cos(A – B ) etc.

Exam Type Question

A

C

B

D 3

5 x

sin (90 + x) = sin 90 cos x + cos90 sin x? ?

sin x = 3/5

cos x

√ (52 – 32)

4

= 4/5

= 1(4/5) + 0(3/5)= 4/5

Calculate Missing Values

using sin(A + B) formula

1.Calculate the exact value of Cos DFG

Cos DFG = Cos(x + y)Cos (x + y) = Cosx Cosy – Sinx Siny

= 1/√5 X 1/√10 – 2/√5 X 3/√10

= 1/√50 – 6/√50

= -5/√50

= - 1/√2

F

D GE

√10

32

X Y1

Using Pythag√5

Key Question

xx

4

32. Find the exact value of

a) Sin DACb) Cos DAC

3. Find the exact value ofSin HFT.

A

B

C

D

3√7/8

1/8

F

G

H

T

x

5√21

2/5